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Microwave Ablation with a Single Small-Gauge Triaxial Antenna: In Vivo Porcine Liver Model¹

¹ From the Departments of Radiology (C.L.B., L.A.S., T.M.F., F.T.L.), Biomedical Engineering (P.F.L.), and Electrical and Computer Engineering (D.W.v.d.W.), University of Wisconsin–Madison, 600 Highland Ave, Madison, WI 53792. Received August 22, 2005; revision requested October 24; revision received January 31, 2006; accepted March 3; final version accepted May 1. Supported by National Institutes of Health grant R21 RR018303-01. Address correspondence to C.L.B. (e-mail: clbrace{at}wisc.edu).

Purpose: To evaluate the performance of a 17-gauge triaxial antenna at microwave ablation in an in vivo porcine liver model.

Materials and Methods: This study was approved by the institutional animal care and use committee. Thirteen female domestic pigs (mean weight, 45 kg) were used. Ablations were performed with a prototype microwave ablation system and triaxial antenna by using a constant, continuous-wave power of 68 W for 2 (n = 6), 3 (n = 6), 4 (n = 6), 5 (n = 6), 6 (n = 6), 7 (n = 13), 10 (n = 7), and 12 (n = 8) minutes. Animals were euthanized after ablation, livers were removed, and ablation zones were sliced and measured for size and roundness. A mixed linear model with animals modeled as random effects was used to test for significant differences in ablation zone metrics among time groups; post hoc tests were used to detect significant differences between time groups.

Results: Mean ablation zone diameters ranged from 2.05 cm ± 0.23 (standard deviation) at 2 minutes to 2.59 cm ± 0.53 at 12 minutes. Thirteen (32%) of 40 ablation zones with mean maximum diameters greater than 3.0 cm were observed at the 5–12-minute time groups. No significant differences in ablation zone diameter were observed among all groups (P > .05), but a trend of increasing diameter with time was noted. Mean isoperimetric ratio (a measure of roundness) for all ablation zones was 0.88 ± 0.02, which indicates minimal heat sinking near vessels.

Conclusion: The triaxial microwave ablation system is capable of creating relatively large, circular zones of ablation in minutes with minimal effects from local blood flow.

© RSNA, 2007

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